1. Technical Field
The present invention relates to a method of manufacturing a gray scale mask and a microlens, a microlens, a spatial light modulating apparatus and a projector, particularly, a technology of a gray scale mask for manufacturing an optical element having a three-dimensional microstructure such as a microlens.
2. Related Art
Up to now, in manufacturing an optical element having a three-dimensional microstructure, used has been a photolithography technology, for example. The photolithography is a technology of applying a resist layer, which is a photosensitive material having a photoreactive characteristic, on a substrate to carry out exposure and development for the purpose of forming a pattern in the resist layer. As a method of forming a desired pattern in a resist layer, used is a technology of exposing a resist through a gray scale mask, for example. The gray scale mask includes plural unit cells whose light transmittance is set so as to correspond to a desired shape of a resist. The light transmittance of a unit cell can be set in accordance with an area aperture rate, which is a rate of the area of an opening in a unit cell, for example. A technology of using a gray scale mask whose light transmittance is set in accordance with the area of an opening is proposed in JP-T-H08-504515, for example.
Depth distribution of a resist shape formed in a resist layer corresponds to distribution of light transmittance in a gray scale mask. It is difficult in some cases to form the resist shape having a high aspect ratio, the aspect ratio being a ratio of the depth to the width, since the light transmittance capable of setting for the gray scale mask is limited in range. Further, it is necessary to form a part of the resist shape corresponding to the vicinity of the outer periphery of a microlens with high accuracy in order to form a microlens capable of efficiently guiding light. On the other hand, a part where the resist depth greatly varies in the two-dimensional direction is extremely difficult to accurately control the resist depth. Accordingly, even a part considered to have a great influence on a performance of the microlens is difficult to be formed with high accuracy. Especially, the higher the aspect ratio of the resist shape is, the larger a range of the resist depth should be made. This causes deterioration in accuracy. As described above, the usual technology has a problem that an optical element having a three-dimensional microstructure such as a microlens is difficult to be formed with high accuracy in some cases.